A good forecaster always has his head in the clouds

It usually comes from the west in this part of the world, and analyzing clouds and what they indicate about weather conditions is a key part of his job in keeping passengers and pilots safe.

As he looks out over runways 05 and 23, Curran can see bald prairie in the foreground and part of the Rocky Mountains about 100 kilometres away.

The clouds, on the other hand, are much closer. Besides the moisture they hold, they carry information that can help in forecasts.

“If you have an advancing front, you can sometimes see that it will push layers of cloud in ahead of it,” says Curran.

“As you get closer and closer to the cold front, if this is active enough, here you’ll have cumulus, or towering cumulus or even thunderclouds, cumulonimbus.

“So you can, in a way, forecast by looking up and saying, oh look, you’ve got advancing cirrus coming toward you, so you know that late today or maybe early tomorrow, the weather is going to change.”

Providing precise weather conditions is the goal in aviation. Pilots need to know conditions at that moment, along the route and at the destination.

Forecasting for agricultural purposes is more complex, Curran admits, and sometimes even cause for amusement.

“The weather channel will give a 14-day forecast, which I find hilarious because no one can forecast 14 days in advance. Nobody.

“We used to have a product that we used called the global forecast, which took everything that we knew now, plugged it into a computer and then said, OK, based on these initial conditions, here’s what’s going to happen. And the farthest we would go is 120 hours, which is five days.

“We told everyone, the pilots, you get beyond three days and I’m making this up. I have no idea.”

Nevertheless, clouds give up clues to weather in the short term and indicate what’s going on in the troposphere and tropopause.

Clouds are water droplets or ice crystals suspended in air. They generally need some kind of particle on which to condense, called condensation nuclei. When enough vapor condenses on enough nuclei, a cloud is formed.

That’s the basis of this old weather rhyme:

Red sky at morning, sailors take warning.

Red sky at night, sailors delight.

Curran says it has truth but it’s not completely reliable.

“When the sun is setting in the west, which, in the northern hemisphere is normally where your weather is coming from … if you have a lot of particulate matter in the sky … it scatters the light and makes it redder.

“That kind of dust is what is called condensation nuclei. It’s really, really tiny and it’s what allows the water in the air to condense and form cloud. So there is some truth, that if you look west during a sunset and its really red, there’s a possibility that something might be coming” by morning.

“It’s not always right, but it’s right often enough.”

Clouds are identified according to their position in the sky, for descriptive purposes.

High clouds include cirrus, cirrocumulus and cirrostratus and are found 5,000 to 13,000 metres above the surface.

Middle clouds include altocumulus and altostratus, found at altitudes from 2,000 to 7,000 metres.

Low clouds, the stratus, stratocumulus and nimbostratus occur between the surface and 2,000 metres.

Then there are those with vertical growth, the big puffy ones called cumulus and cumulonimbus, which can occur anywhere be-tween the surface and 13,000 metres.

Cumulus clouds commonly have flat bases and heaped tops, the “ice cream castles” of Joni Mitchell’s song. But she might also mean towering cumulus, which have brilliant white tops and grayish bottoms because their thickness doesn’t allow sunlight to penetrate to the bottom, said Curran.

“Under these towering cue, you’re going to have rain and if it continues building, you get a CB and a thunderstorm and lots of rain.”

About the author

Barb Glen's recent articles


Stories from our other publications